.wrapper {
  padding: 16px;
}

.box_5 {
  width: 100px;
  height: 100px;
  border-radius: 20px;
  background-color: aqua;
  box-shadow: 15px 15px 0 0 lightblue;
  animation: shadow5 5s infinite linear;
}
@keyframes shadow5 {
  50%{
    box-shadow: 15px 15px 0 0 lightcoral;
  }
}